The application of mechanisms in medical devices is accompanied with an increasing demand for mechanical components or elements that require only a restricted volume. This is true especially of portable medical devices that are used by patients and have to be everywhere available. If a mechanism of restricted dimensions requires the application of a spring force, the operation of the mechanism is essentially affected by the properties of the spring element. Therefore, a number of different spring types are used in medical devices or have been suggested for an application in conjunction with medical devices, especially with injection or infusion devices.
U.S. Pat. No. 7,462,169 B2 discloses a safety shield system for an injection pen needle. A mechanically operating part of the injection pen needle can be equipped with a wave spring. U.S. Pat. No. 7,220,245 B2 discloses an infusion apparatus, which is furnished with a flow control means, for which, inter alia, the use of wave springs is recommended.
EP 1 704 883 B1 and EP 1 704 884 B1 disclose devices for administering a fluid product in doses. An embodiment comprises a cylindrical drive member having a thread inside and an output member as well as an adjustment element both having a screw thread of the same pitch. A spring is arranged between the drive member and the adjustment element in order to enhance the friction between the threads. The drive member and the adjustment element can have structures inhibiting a rotation of the adjustment element within the drive member. A further embodiment comprises a screw-like drive member and a wave spring arranged between the housing and a transfer element, which is in contact with a drive ring of the drive member. The transfer element can be rotationally fixed with respect to the housing. The transfer element and the drive ring preferably form a pair of sliding faces.